1. Field of the Invention
In three-wire electrical load systems of the type normally used in residential wiring, it is desirable to avoid blowing fuses or tripping circuit breakers by applying excessive loads to a single branch circuit. This invention senses different circuit phases and prevents overloading any one circuit in a multi-phase system. This invention does not provide fault protection.
2. The Prior Art
U.S. Pat. No. 4,532,569 Salcedo shows a relay 12 connected across opposite phases of a 125-250 volt service line. The coil of a relay 27 senses the voltage across the two power lines. The apparatus through the relay detects the voltage difference between the power signals carried on the two wires which carries positive and negative power signals. When the proper voltage is detected, relay contactor 25 closes, connecting the power to various loads. In this device, the contactor 55 switches the +125 volt, the -125 volt, and neutral lines in and out of the circuit simultaneously. There is no concern for or provision for prevention for overload in either the +125 volt or the -125 volt line.
U.S. Pat. No. 3,944,891 McDonald et al discloses a circuit for interconnecting a load only when voltage conditions from the system are appropriate. There is a logic circuit which includes a means for providing ground fault protection. This reference utilizes a logic circuit including a switching means for interrupting current flow and utilizes a polarity response means for synchronizing conductivity to the switch means when conditions of opposite voltage polarity are in the lines L1 and L2 relative to the line neutral.